1. Field of the Invention
This invention relates generally to communications systems using fax devices for transmission of fax information through packet switching networks and particularly to transmission of fax information wherein modulation/demodulation of fax information occurs independently of and remotely from the protocol implementation used prior to transmission of information.
2. Description of the Prior Art
Facsimile (Fax) machines are commonly employed in modern communications systems. Typically, two fax machines are in communication with each other exchanging messages faxed by users thereof. The messages transmitted by a fax machine are generally in analog format and are often transmitted through a Public Switching Telephone Network (PSTN) as depicted in FIG. 1.
In FIG. 1, fax machine 12 is shown to be in communication with fax machine 14 through the PSTN 16. Transmission line 18 couples the fax machine 12 to the PSTN 16, which is in turn linked to the fax machine 14 via the communication line 20. Also shown in FIG. 1 are the various components which comprise a typical fax machine. A protocol subsystem 22 within fax machine 12 operates to implement various protocols, such as the T.30 and T.4/T.16 protocols, which are commonly used in the industry. Additionally, a data pump 24, a scanner 26 and a memory 28 are shown included in the fax machine 12.
Messages are exchanged between fax machines using protocol information either located within the hardware or implemented by execution of the software within the fax machine. One of the protocols is the protocol T.30 which carries information such as that relating to the size of the fax page, the type of compression technique being employed on the fax data and the like.
Other protocols, such as the T.4/T.6, are used for transferring information regarding fax pages and the actual content of the fax message. Information in conformance with the various protocols mentioned hereinabove is modulated prior to transmission thereof. The modulation protocols used to send fax messages are sometimes referred to as V-series modulation protocols such as V.21, V.29, V.17, V.33 and V.27ter. The various V-series modulations differ according to their speed of transmission. For instance, the T.30 protocol is transmitted using the V.21 modulation protocol which causes operation at a relatively slow speed of 300 bits/sec whereas the T.4/T.6 protocols are transmitted using faster modulation protocol, such as the V.17, V.29, V.33 and V.27ter. In FIG. 1, the part of the fax machine 12 which performs the V-series modulation and demodulation is the data pump 24. Demodulation applies to the case when fax machine is receiving rather than transmitting data. That is, information being received is demodulated to extract the original fax information.
In addition to the protocol subsystem 22 and the data pump 24, the fax machine 12 generally includes the scanner 26 and the memory 28. Scanner 26 scans pages of information that are to be faxed as the pages are passed through the fax machine and transforms them into black and white pixels. The pixel information is then encoded and stored in the memory 28 of the fax machine.
Alternatively, a fax machine could be incorporated in a personal computer (PC). In such a case the data pump component of the fax machine is placed on a modem card and the component of the fax machine which executes the T.30 and T.4/T.6 protocols is a software program on the PC. The modem card is physically connected to the PC through a cable and for this reason cannot be placed in a location too remote from the PC such as in a network.
Yet another mode of communication between the fax machines 12 and 14, not shown in FIG. 1, is through a network such as the Internet or any other wide area network (WAN). An example of the latter is a WAN used by Cisco Systems, Inc. of San Jose, Calif. In such a mode of communication, referred to as fax relay, the originating fax machine is coupled to a first PSTN with the latter being linked to the network. The network is in turn linked to a second PSTN, which is coupled to the receiving fax machine so that the fax messages between the two fax machines are transmitted through the network. The network remains transparent to the communicating fax machines so that the fax machines communicate with each other in exactly the same way as that which is shown in FIG. 1.
Sending fax messages via fax relay can be considerably less expensive than the method of communication shown in FIG. 1 where the fax message is sent through the PSTN 16. In particular, if the two communicating fax machines are located remotely with respect to each other, i.e. in different parts of the world, sending fax messages through a PSTN requires paying expensive international toll rates whereas using fax relay requires paying local toll rates, which are obviously substantially less than international rates. For instance, the fax message could be sent through the Cisco WAN where the only expense is in sending the message from the local PSTNs to the fax machines. Presently, Cisco Systems manufactures products equipped with appropriate software to support fax relay. Examples of such products include access server (AS) models C2600, C3600, AS5300 and AS5800.
Access servers are located at the edges of the network. In fax relay, when a fax message is received by an access server, such as the AS5300 having fax relay capability, the message is demodulated and sent across the network to a receiving access server which is physically closest to the receiving fax machine. Messages transferred between access servers through the network are in packet form. Packets are unbundled by the receiving access server and subsequently remodulated into the original fax message and sent to a local PSTN using T.30 and T.4/T.6 protocols. The PSTN then sends the fax message to the receiving fax machine. Messages are sent from one point in the network to another point in the network using a propriety proprietary fax relay protocol or a standardized protocol such as the T.38 protocol.
An access server, such as the AS5300, does not decode the fax messages in the T.30 and T.4/T.6 protocols and the original fax information that is encoded in these protocols passes from one access server to another transparently. Consequently, no change in the contents of the fax messages takes place as the messages are transmitted through the network via the access servers. It is the fax machine which can implement the T.30 and T.4/T.6 protocols, using the protocol subsystem 22 of FIG. 1, and recover the actual fax message. Using the network to send fax messages is referred to as fax relay due to relaying of the faxed messages from one point of the network to another with no alteration in the contents of the faxed message while it travels through the network.
Fax relay is a one-to-one method of transmitting fax messages between two fax machines. Accordingly, there is an originating fax machine which dials the number of a receiving fax machine and sends the message through an intermediate network. However, it is desirable to send fax messages from the originating fax machine to an access server which may be located at any point in the network. Once received by the access server, the message could either be sent to a receiving fax machine or to an email recipient in the from of an email message. Alternatively, the message could simply be stored somewhere in the network for later delivery. The latter option is particularly useful when the receiving fax machine is busy in which case the fax message is still received by the network and stored somewhere therein. The fax message can then be transmitted to the receiving fax machine at a later time when the latter is no longer busy. Such a mode of transmitting fax messages has the effect of distributing the functionality of the fax machine throughout the network.
Therefore, the need arises to distribute the functionality of a fax device through a packet switching network thereby increasing system capacity and allowing for readily altering features of a fax device without the need for additional hardware.